Furnace



J. C. WHITE May 8, 1934.

FURNACE Filed Deo. l5, 1930 4 Sheets-Sheet l NII v INVENTOR.

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,Si @DE May 8, 1934.

J. C. WHITE FURNACE Filed Dec. l5, 1930 4 Sheets-Sheet 2 HET INVENToR. Job/7 C M//We 'BY/@nf A TTORNEYS.

May 8, 1934. J. C. WHITE 1,957,921

FURNACE Filed Deo. l5, 1950 4 Sheets-Sheet 5 FIEL INVENTOR. \/0/7/7 C W/z/Ie A TTORNEYS.

Fatenteci May 8, 1934 UNE'ED STATES PATENT QFFIC 1 Claim.

My invention relates to furnaces and is particularly applicable to furnaces adapted to utilize comminuted material for fuel, such as saw-dust, shavings, pulverized coal, and the like.

In establishments engaged in the lumber indusl try, where saw-dust and shavings are plentiful,

it is common to use these materials for fuel and not infrequently they are used to the exclusion of all other types of fuel. it has been customary to deliver the fuel to the furnace through a circular opening in the top of the fire-box from which it drops onto a substantially horizontal grate. The fuel thus fed into the rebox forms a conical ple having a slope corresponding to the angle of normal repose of the material, thereby forming a bed of varying thickness. Air passing upwardly through the grate and through the pile of fuel follows the path of least resistance and consequently combustion is supported more readily along the peripheral edge of the pile than at the central portion of the pile. As a result the burning is not uniform throughout the pile and the fuel burns faster in an annular ring near the base of the pile. Non-uniform burning of -the fuel in this manner gives rise to many serious disadvantages. The grate is unevenly heated causing undesirable warping and rapid deterioration. Deposits of slag from foreign matter in the fuel accumulate in the openings vof the grate near the area of greatest activity, thereby greatly reducing the efficiency of the furnace and necessitating more frequent cleaning.

Heretofore, it has been a common practice to employ a grate made of cast iron for supporting the fuel and in order to prevent warping or melty ing of the grate, precautions were taken to keep l terial, such as fire brick, and when the fuel support is exposed to conditions which cause the temperature of the support to reach a relatively high value.

It is one object of'my invention to provide a furnace in which comminuted fuel, such as 1 saw-dust and the like can be burned at increased efficiency.

A further object is to provide a furnace m which comminuted fuel can be burned more eveng ly, and uniformly.

A further object is to provide a furnace in which novel means is provided for volatilizing comminuted fuel and for burning the resulting gases under the most advantageous conditions.

A still further object is to provide a furnace of the character described in which complete combustion of the fuel is effected at a relatively low maximum temperature, thereby increasing the useful life of the furnace lining.

A still further object is to provide a furnace in which accumulations of slag and the like can be removed without interrupting operation of the furnace.

Still another object is to provide a furnace which is more convenient to operate and in which the cost of maintenance is reduced.

These and other objects and advantages are attained in the embodiments of the invention illustrated in the drawings in which:

n Fig. 1 is a longitudinal cross section of a furnace incorporating certain principles of my invention.

Fig. 2 is a cross section taken on the line 2 2 of Fig. l.

Fig. 3 is a front elevation partly in section of a modification.

Fig. 4 is a cross section taken along the line 4-4 of Fig. 3.

Fig. 5 is a cross section taken on a plane parallel to the front of a furnace illustrating another modification. v

In its preferred form my invention comprises a furnace having a fire boX within which one or more fuel supports are disposed, each support being inclined to the horizontal, preferably at an angle which substantially corresponds with the angle of normal repose of the fuel which is to be used. Fuel such as sawdust deposited gravitationally on the support forms an evenly distributed bed thereon and a supply of air is provided for supporting combustion of the fuel.

Preferably, a plurality of air passages extend through the support at an angle which increases the length of the passages andthe air conducted through the passages is caused to move at a relatively slow rate, thereby forming heat confining chambers in the support which preclude rapid cooling of the support. Also, the fuel support is preferably made of heat absorbing material, such as fire brick, so that heat will be effectively stored and retained by the support.

In operation of the furnace a relatively thick bed of fuel such as sawdust is employed, thereby further retarding the flow of air through the fuel support` which results in effectively preheating the air as it passes through the fuel support. The

Y' front end of a boiler' 23.

heated air, in addition to supplying oxygen 'to support combustion of the fuel, also serves to volatilize the fuel. Consequently, there is little or no surface fire and the burning occurs in the volatilized combustible gases. For effecting this condition, surpius oxygen is avoided and only sulficient air to support complete combustion is delivered to the fuel. I have found that most eicient operation is obtained when the air supply is regulated so that burning will occur in the volatile gases approximately four feet from the surface of the fuel bed.

Referring now to the drawings and particularly to Figs. 1 and 2 thereof, I have shown a furnace provided with a fire box 16 having a relatively large combustion chamber, commonly known as a Dutch oven. In the embodiment of the invention shown in Figs. 1 and 2 the top wall 17 of the re box is approximately at the same level as, or slightly lower than a floor 13 of the structure in which the furnace is placed. The top wall 17 can be supported in any suitable manner between side walls 19 and 21 of the fire box and can extend from the front wall 22 to a point adjacent the Near the rear of fire box 16 is a bridge wall 24 which serves to deflect the hot gases of combustion toward the boiler 23.

The furnace is particularly adapted for burning saw-dust and the like and for feeding the fuel to re box 16, spouts 26 and 27 are provided which extend from a hopper 31 or other suitable container` for a supply of the fuel, to elongated openings 28 and 29 in the top of the fire box. Openings 23 and 29 preferably extend across the full width of the re box and each of the spouts 26 and 27 communicating therewith has an outlet which is co-extensive with these openings. Adjustable gates 32 and 33 are provided for control ling the iiow of saw-dust in spouts 26 and 27 respectively. Fuel passing through openings 28 and 29 showers down upon the uppermost portions of a pair of inclined fuel supports 36 and 37 disposed within the fire box.

The fuel support 36 comprises a plurality of layers of refractory hollow tile superposed on one another. Each layer extends between side walls 19 and 21 of the fire box and projects into the fire box a distance slightly less than the layer immediately below it. Thus, in Fig. 1 I have shown the layers as progressively decreasing in size toward the top, the inner sides of the layers forming an inclined stepped support for the fuel and the outer sides being substantially flush with the front wall 22 of the nre box. Each layer i is so constructed that a plurality of air ducts 39 are formed therein which serve to con-duct air from the front of the furnace into the bed of the fuel resting on support 36. For regulating the amount of air passing through each duct 39, a damper 41 can be provided which is adapted to vary the effective opening of each duct. If desired, each damper can be provided with means for actuating it separately, but in Fig. 1 I have shown a plurality of dampers 41 interconnected by rod 42 which extends through floor 18 to a point where it is conveniently accessible to an attendant. By actuating rod 42 the dampers controlled thereby can be adjusted to any desired position.

Fuel support 37 is likewise formed of a plurality of superposed layers of refractory hollow tile and this support also presents an inclined stepped surface to the interior of the re box. Support 37 is provided with a plurality of air ducts similar to the ducts in support 36 and air is delivered to the ducts in support 37 through an arched passage 43 extending beneath support 36 and under fire box 16 to a chamber 44 at the rear of the re box with which the ducts communicate. The flow of air through passage 43 is controlled by a damper 46 which can be actuated by a linkage 47 extending upwardly through floor 18 or by any other suitable means. Disposed on either side of passage 43 are passages 48 and 49 which serve as ash pits. An opening 50 is provided in the upper wall of each of these passages through which ashes and slag can drop. For insuring an ample air supply to the rear fuel support 37 a plurality of auxiliary air ducts 5l can be provided which extend below passages 43, 48 and 49 and which communicate with chamber 44.

Sawdust fed into the fire box 16 through the spouts 26 and 27 tends to form a pile of fuel having a definite slope which is determined by the normal angle of repose of the sawdust. Heretofore, the tendency of the sawdust to pile up in this manner has been highly objectionable and has resulted in inefcient operation of furnaces utilizing saw-dust as a fuel. In the exercise of my invention, however, I make use of this characteristic of the fuel to obtain a relatively uniform bed of fuel by making the general slope or pitch of the surfaces of the fuel supports 36 and 37 approximately equal to the angle of normal repose of the fuel. When sawdust is de posited on the upper portions of supports 36 and 37, it gravitationally flows to form a uniformly thick bed of the material which slopes downwardly from the front of the furnace toward the center over support 36 and which slopes downwardly from the rear of the re box toward the center over support 37. By this construction the burning is uniform throughout the entire fuel bed and consequently the efficiency of the furnace is increased.

For facilitating cleaning of the fuel supports I have shown the opening 28 as being sloped in the general direction of the stepped surface of fuel support 36. This construction permits the insertion of a rake or other implement through opening 28 for removing slag and the like from support 36. As a further aid to the cleaning of the furnace, the air ducts in support 37 can be disposed in substantial alignment with the ducts in support 36, thereby allowing the insertion of a cleaning implement through supports 36 and 37 from the front of the furnace. Preferably, air passage 43 is made large enough to allow admittance of a person to chamber 44 for cleaning the ducts in fuel support 37 from the other end of the fire box, when it is desired to clean these ducts more thoroughly. Thus, the various parts of the fuel supports are readily accessible to an attendant. The greater portion of slag which is formed nds its way to the entrance in passages 48 and 49 by reason of the slope of supports 36 and 37 and it is not necessary therefore, to clean the nre box as frequently as in other constructions where substantially horizontal grates are employed. The ducts in supports 36 and v37 are shown as being inclined slightly downwardly toward the interior of the re box, thereby causing molten slag to flow inwardly toward the ash pits rather than to clog the ducts by flowing in the other direction.

In addition to causing the formation of a relatively uniform bed of fuel, the inclined stepped supports 36 and 37 serve to increase the operating efficiency of the furnace by'effectingmor'e rapid volatilization of the fuel than when a horizontal support is employed. On account of the general inclination of the surface of the supports from horizontal, a greater area is exposed to the heat within the' fire box 16 and accordingly the supports 36 and 37 are raised to a higher temperature than would be the case with horizontal supports or grates. Being preferably formed of fire brick and therefore of heat absorbing material, heat is stored in the supports and they are not subject to rapid cooling by the air delivered through the ducts 39. Ducts 39 are relatively long and since they are inclined to the surface of the fuel bed, air is retarded to a certain extent as it passes through the ducts. Best results are obtained if only sufficient air is supplied to support complete combustion without a surplus of oxygen and in order to further retard the passage of air I prefer to employ a relatively thick fuel bed. By controlling the amount of air admitted to the ducts by adjustment of the dampers 4l and 46, the most efficient operating conditions for the furnace can be obtained.

By retarding the flow of air through ducts 39 in this manner, the air is effectively preheated while the temperature of the supports is maintained at a relatively high, yet safe, value. The heated air, as it passes through the fuel bed effects volatilization of the fuel and a mixture of air and volatile gases is formed which does not mixture which ignites at a distance -between four and six feet from the surface of the fuel bed. Under these conditions the temperature at the inner portions of the fuel ducts 39 was approximately 2400o F. and the walls and ceiling of the fire box 16 were also approximately 2460D F. Heretofore, in furnaces in which surface fire was present in addition to some burning of the volatile gases, the walls and ceiling of the fire box commonly reached a temperature of approximately 3000" F., which is dangerously close to the melting point of fire brick. With a furnace constructed in accordance with this invention, more complete combustion and higher elciency result and at the same time the maximum temperature is maintained at a safe value.

Among the factors contributing to the increased efficiency of my furnace are the thorough mixing of the volatile gases and air before ignition takes place and the retardation of the air entering the furnace and of the gases of combustion leaving the furnace. An excess of air results in an increase of free oxygen in the fiue gas, with the consequent loss in efficiency. A deficient supply of air increases the carbon monoxide content and the combustion will not be complete. Even when the theoretically correct amount of air is supplied, combustion will be incomplete if the volatile matter is not thoroughly mixed with the air before combustion takes place. In a furnace constructed in accordance with my invention the air supply can be accurately controlled and is preheated before entering the fuel bed. After volatilization of the fuel, the air is given ample opportunity to become thoroughly mixed with the volatile gases, thereby insuring complete combustion.

Repeated tests on a furnace constructed in accordance with this invention have indicated that combustionl is practically ideal. With sawdust having moisture, flue gas analysis. consistently showed 17.5% CO2; 2.5% oxygen and Zero CO. The significance of these figures becomes apparent when it is considered that heretofore from 15 to 16 per cent CO2 was all that could be attained under the very best working conditions and that the average range for general practice lies between l0 per cent and 14 per cent CO2.

If desired an outlet 52 can be provided in bridge wall 24, the effective opening of which can be controlled by a damper 53 actuated by any suitable means, such as a chain 54 passing about pulleys 56, 57 and 58 through passage 43 and up through licor i8. Outlet 52 serves as a bypass for part of the air entering chamber 44 and its use enables more accurate control over the air flowing through the ducts in support 37.

In Figs. 3 and 4 I have shown a modification in which the fuel supports slope downwardly from two opposite sides of the fire box toward the center of the same. Thus, I have shown a pair of fuel supports 63 and 64 sloping downwardly from the side walls 65 and 66 of a re box 67 and which are carried by a plurality of columns 61 and 62. A supporting framework 68 made of any suitable material, such as cast iron, can be provided for each of the fuel supports 63 and 64. Fuel supports 63 and 64 have an inclined stepped surface, the general pitch of which is approximately equal to the angle of normal repose of the sawdust being used in the furnace. Fuel is delivered to the upper portions of each of the supports 63 and 64 through a pair of spouts 69 and 70 by way of a pair of openings 7l and 72 in the roof of the fire box. rlhe lower ends of the fuel supports 63 and 64 are spaced apart and the opening 73 formed by this construction permits ashes and slag to drop into an ash pit 74 disposed below the opening. A door 75 can be provided on the front of the furnace which permits access to ash pit 74, for cleaning purposes. An air inlet controlled by a suitable damper 76 on the front wall of the furnace permits passage of air into a chamber 77 disposed behind the fuel support 63 and with which the air ducts in support 63 communicate. A similar air passage is provided for conducting air into chamber 78 into which the ducts of fuel support 64 extend. To facilitate cleaning of the furnace a door 79 is provided for each of the chambers 77 and 78 through which an attendant can gain admittance to clean the ducts in each of the fuel supports. A door 8l can be provided on one of the side walls of the furnace in a position which permits insertion of a rake through the ducts in support 64 and also through the ducts in fuel support 63, the ducts in both fuel supports preferably `being in substantial alignment for this purpose. The iiame and hot gases of combustion from the nre can be directed into the heating chamber 82 of a boiler 83 in any desired manner.

At the end of fire box 67 and adjacent the entrance of the heating chamber 82, I have shown a downwardly extending deiiecting member 80 against which the combustible mixture of volatile gases and air is adapted to impinge and be defiected. When the combustible gases arrive at this point they are in highly critical state and are on threshold of bursting into flame and I have found that by providing a deflecting member to disturb the path of the gases a turbulence is caused which is sufficient to effect ignition of the gases. By this expedient the fiame can be produced at any desired point within certain limits, thereby affording a convenient control over the behavior of the fire and resulting in a further increase in efficiency. It is to be understood that other forms of deiiecting members can be employed to effect the desired disturbance. If desired, the same result can be 0btained by so constructing the furnace that a special deecting member is not required. For example, in Fig. 1 I have shown the bridge wall 24 as extending into the path of the combustible gases at a point adjacent the forward end of the boiler 23 where it is desirable to have the burning take place. By properly adjusting the amount of air delivered and its velocity a mixture can be obtained which will be in a critical condition when it reaches the bridge wall 24 and the turbulence set up thereby will cause the gases to burst into flame at that point. The air delivered to the fuel can be very closely regulated by the means provided for this purpose heretofore described and since the fuel openings are normally sealed with fuel, none of the air entering the furnace is lost by leakage through these openings nor is any air permitted to enter the furnace by this path. Thus, all air entering the furnace must pass through the fuel bed and there are no openings in the structure through which uncontrolled air can enter and thereby disturb the proportions of the inflammable mixture of gases.

In Fig. 5 I have shown a modification in which a pair of fuel supports 84 and 85 are provided which slope downwardly from the center of a re box toward two opposite sides thereof. The fuel supports are mounted on suitable columns 86 and 87 and are preferably so constructed that a single passage 88 is formed which communicates with all the air ducts in both fuel supports. A suitable door can be provided on the front wall of the furnace for controlling the amount of air passing into passage 88 and this door is preferably large enough to permit entrance of a man into passage 88 for cleaning the ducts.

In this embodiment of my invention fuel is delivered into the fire box at the upper portions of both supports 84 and 85 by means of a spout 89 extending through an elongated opening in the roof of the re box. Disposed adjacent the longitudinal sides of spout 89 are a pair of regulating members 92 and 93. Members 92 and 93 are composed of any suitable re resistant material and are preferably supported for Vertical adjustment within the elongated opening in roof 91 of the re box.

The slope of the upper surface of each of the supports 84 and 85 is preferably approximately equal to the angle of normal repose of the sawdust, as in the embodiments of the invention heretofore described, and fuel passing through spout 89 flows along the surface of the supports to form a bed of fuel of substantially uniform thickness. When the thickness of the bed of fuel becomes such that the surface of the bed reaches the bottom edge of either member 92 or 93, fuel ceases to flow in the direction of the contacting member. When the surface of the fuel bed engages both members 92 and 93, the fuel passage becomes clogged and the fuel piles up in spout 89 as sho-wn in Fig. 5. By means of nuts 94 members 92 and 93 can be raised or lowered and the position of these members relative to supports 84 and 85 will determine the thickness of the fuel bed on the supports. As the fuel burns away, the fuel bed recedes from members 92 and 93 thereby allowing more fuel to flow from spout 89. By this expedient the fuel bed can be kept automatically at any desired thickness as long as there is a surplus of fuel in spout 89. The greater portion of the ash and slag which is formed ows down the inclined surfaces of supports 84 and 85 and accumulates at the bottom of the re box near the side walls where it is readily accessible for removal.

While I have shown and described certain preferred embodiments of my invention, it is to be understood that I do not wish to be limited thereto, since the invention as defined in the appended claim can be embodied in a plurality of other forms.

I claim:

In a furnace of the character described, a re box comprising side walls, a roof, a front wall, and a bridge wall opposite said front wall and defining with said roof an exit for combustion gases, a pair of opposed inclined fuel supports, said fuel supports having opposed air passages extending therethrough in substantial horizontal alignment, one support extending downwardly from adjacent the top of the front wall and the other support extending downwardly from adjacent the top o-f the bridge wall, the lower endsV of said supports being spaced to form therebetween an ash discharge passage, means in saidv roof for depositing fuel on the uppermost portion of each fuel support, and means for delivering air beneath each fuel support.

JOI-IN C. WHITE. 

